High density titanium carbide ceramics

ABSTRACT

Disclosed are high density, sintered titanium carbide bodies comprising 2-10 wt % silicon carbide, up to 2 wt % free carbon and 88 to 98 wt % titanium carbide.

This is a divisional of application Ser. No. 08/283,339 filed on Aug. 1,1994 now U.S. Pat. No. 5,447,893.

BACKGROUND OF THE INVENTION

This invention relates to the preparation of high density titaniumcarbide ceramic bodies by the pyrolysis of mixtures comprising titaniumcarbide powder and preceramic organosilicon polymers.

Titanium carbide ceramic bodies are known in the art. They have foundparticular utility, for example, as wear parts and in the nuclearindustry because of their high hardness, resistance to wear and nuclearproperties. Early methods for producing these bodies involvedhot-pressing titanium carbide powder at temperatures up to 2300° C. Thismethod, however, has a number of disadvantages. In the first place, themethod does not produce green bodies and, as such, does non allow forgreen machining. Secondly, the process is expensive in that it requiresthe use of high pressure during sintering. Finally, it is difficult toform bodies of complex size and shade by hot pressing methods.

An alternative approach to producing titanium carbide bodies is to usefugitive binders to form green titanium carbide bodies and thenpressureless sintering these green bodies. In this approach, however,the binder must be pyrolyzed out of the bodies. As such, the processtakes additional time and the ceramic bodies undergo significantshrinkage which may result in warpage or cracks.

Yajima et al. in U.S. Pat. No. 4,289,720 teach a process for theformation of ceramic fired bodies. The process comprises moldingmixtures of organosilicon polymers and ceramic powders to form greenbodies followed by pyrolyzing the green bodies to form ceramic bodies.The reference, however, lists over 150 ceramic powders (includingtitanium carbide) whereas the examples only show densification ofsilicon carbide, silicon nitride and boron carbide. Moreover, thereference only teaches temperatures up to 2000° C. (temperatures in therange of 1550°-1800° C. are preferred) (col. 9, lines 1-4). The presentApplicant has discovered that such temperatures are not sufficient tocomplete the polymer pyrolysis. As such, the density of the bodies inthe reference is less than those of the present application.

The object of the present invention is to provide a method for producinghigh density, high strength titanium carbide ceramic bodies. The presentinventor has unexpectedly discovered that such ceramics can be obtainedby sintering a mixture comprising a preceramic organosilicon polymer andtitanium carbide powder.

SUMMARY OF THE INVENTION

The present invention relates to a method for preparing a sinteredtitanium carbide ceramic body. The method comprises blending titaniumcarbide powder and a preceramic organosilicon polymer to a uniformmixture. The preceramic organosilicon polymer is one which provides atleast a stoichiometric amount of carbon based on the silicon content.The uniform mixture is then formed into the desired shape to obtain ahandleable green body. The handleable green body is then sintered in aninert atmosphere at a temperature greater than 2000° C. to obtain asintered body with a density greater than about 4.2 g/cm³.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the preparation of high densitysintered titanium carbide bodies from preceramic organosilicon polymersand titanium carbide powder. The sintered bodies produced by thepractice of this invention have densities greater than about 4.2 g/cm³.Such highly densified bodies are useful, for example, in wear marts andthe nuclear industry.

As used in the present application, the theoretical density of titaniumcarbide is 4.94 g/cm³. As discussed infra, however, the ceramic bodiesof the present invention generally contain some SiC and carbon in theintergranular pores. The theoretical amount of SiC in a ceramic body istaken into consideration when calculating theoretical densities.

The first step of the present invention comprises blending theorganosilicon polymer with the titanium carbide powder. Theorganosilicon polymers useful in this invention are generally well knownin the art. Organosilicon polymers with a significant ceramic char yieldare preferred because the amount of binder shrinkage that occurs uponpyrolysis decreases as the char yield increases. Preferably, therefore,the ceramic char yield is greater than about 20 weight percent. Morepreferably, organosilicon polymers with ceramic char yields greater thanabout 35 weight percent are employed. Most preferably, organosiliconpolymers with ceramic char yields greater than about 45 weight percentare employed.

The organosilicon polymer must also yield a ceramic char containing atleast enough carbon to form silicon carbide with the silicon present inthe char (hereafter referred to as a "stoichiometric amount"). Excesscarbon in the char is often preferred because it assists in removingoxygen and thus, in the densification of the ceramic body. This excesscarbon is referred to as "free carbon" (i.e., excess carbon present inthe char over the amount of carbon needed to form silicon carbide withthe silicon present in the char). It is often preferred that the ceramicchar contain at least 10 weight percent free carbon. It is often morepreferred that the ceramic char contain at least 25 weight percent freecarbon.

Organosilicon polymers within the scope of this invention includepolysiloxanes, polysilazanes, polysilanes, and polycarbosilanes. If theorganosilicon polymer is an organopolysiloxane, it may contain units ofgeneral structure [R₃ SiO₀.5 ], [R₂ SiO], [RSiO₁.5 ], and [SiO₂ ] whereeach R is independently selected from the group consisting of hydrogen,alkyl radicals containing 1 to 20 carbon atoms such as methyl, ethyl,propyl etc., aryl radicals such as phenyl, and unsaturated alkylradicals such as vinyl. Examples of specific organopolysiloxane groupsinclude [PhSiO₁.5 ], [MeSiO₁.5 ], [MePhSiO], [Ph₂ SiO], [PhViSiO][ViSiO₁.5 ], [MeHSiO], [MeViSiO], [Me₂ SiO], [Me₃ SiO₀.5 ], and thelike. Mixtures of organopolysiloxanes may also be employed.

The organopolysiloxanes of this invention can be prepared by techniqueswell known in the art. The actual method used to prepare theorganopolysiloxanes is not critical. Most commonly, theorganopolysiloxanes are prepared by the hydrolysis oforganochlorosilanes. Such methods, as well as others, are described inNoll, Chemistry and Technology of Silicones, chapter 5 (translated 2dGer. Ed., Academic Press, 1968).

The organopolysiloxane may also be substituted with various metallogroups (i.e., containing repeating metal-O-Si units). Examples ofsuitable compounds include borosiloxanes and alumosiloxanes which areboth well known in the art. For instance, Noll, Chemistry and Technologyof Silicones, chapter 7, (translated 2d Ger. Ed., Academic Press, 1968)describes numerous polymers of this type as well as their method ofmanufacture. Additionally, Japanese Kokai Patent No. Sho 54[1979]-134744granted to Tamamizu et al., U.S. Pat. No. 4,455,414 granted to Yajima etal. and U.S. Pat. No. 5,112,779 granted to Burns et al. also describethe preparation and utility of various polymetallosiloxanes as bindersfor SiC powder. All of these references are hereby incorporated byreference.

If the preceramic organosilicon polymer is a polysilazane, it maycontain units of the type [R₂ SiNH], [RSi(NH)₁.5 ], and/or ##STR1##where each R is independently selected from the group consisting ofhydrogen, alkyl radicals containing 1 to 20 carbon atoms such as methyl,ethyl, propyl etc., aryl radicals such as phenyl, and unsaturatedhydrocarbon radicals such as vinyl and each R', R", and R'" isindependently selected from the group consisting of hydrogen, alkylradicals having 1 to 4 carbon atoms, aryl radicals such as phenyl, andunsaturated hydrocarbon radicals such as vinyl. Examples of specificpolysilazane units include [Ph₂ SiNH], [PhSi(NH)₁.5 ], ##STR2##[MeSi(NH)₁.5 ], [Me₂ SiNH], [ViSi(NH)₁.5 ], [Vi₂ SiNH], [PhMeSiNH],[HSi(NH)₁.5 ], [PhViSiNH], [MeViSiNH], and the like.

The polysilazanes of this invention can be prepared by techniques wellknown in the art. The actual method used to prepare the polysilazane isnot critical. Suitable preceramic silazane polymers or polysilazanes maybe prepared by the methods of Gaul in U.S. Pat. Nos. 4,312,970 (issuedJan. 26, 1982), 4,340,619 (issued Jul. 20, 1982), 4,395,460 (issued Jul.26, 1983), and 4,404,153 (issued Sep. 13, 1983), all of which are herebyincorporated by reference. Suitable polysilazanes also include thoseprepared by the methods of Haluska in U.S. Pat. No. 4,482,689 (issuedNov. 13, 1984) and Seyferth et al. in U.S. Pat. No. 4,397,828 (issuedAug. 9, 1983), both of which are hereby incorporated by reference. Otherpolysilazanes suitable for use in this invention can be prepared by themethods of Cannady in U.S. Pat. Nos. 4,540,803 (issued Sep. 10, 1985),4,543,344 (issued Sep. 24, 1985), Burns et al. in J. Mater. Sci, 22(1987), pp 2609-2614, and Burns in U.S. Pat. Nos. 4,835,238, 4,774,312,4,929,742 and 4,916,200, which are all incorporated herein in theirentirety.

The polysilazane may also be substituted with various metal groups(i.e., containing repeating metal-N-Si units). Examples of suitablecompounds include borosilazanes which are known in the art. Theseinclude, but are not limited to, those described in U.S. Pat. No.4,910,173 granted to Niebylski, those described by Haluska in U.S. Pat.No. 4,482,689, those described by Zank in U.S. Pat. Nos. 5,164,344,5,252,684 and 5,169,908, those described by Funayama et al., in U.S.Pat. No. 5,030,744, those described by Seyferth et al., J. Am. Ceram.Soc. 73, 2131-2133 (1990), those described by Noth, B. Anorg. Chem. Org.Chem., 16(9), 618-21, (1961), and those described by Araud et al. inEuropean Patent No. 364,323, which are all incorporated herein byreference in their entirety.

If the preceramic organosilicon polymer is a polysilane, it may containunits of general structure [R₃ Si], [R₂ Si], and [RSi] where each R isindependently selected from the group consisting of hydrogen, alkylradicals containing 1 to 20 carbon atoms such as methyl, ethyl, propyletc., aryl radicals such as phenyl, and unsaturated hydrocarbon radicalssuch as vinyl. Examples of specific polysilane units are [Me₂ Si],[PhMeSi], [MeSi], [PhSi], [ViSi], [PhMeSi], [MeHSi], [MeViSi], [Ph₂ Si],[Me₂ Si], [Me_(Si) ], and the like.

The polysilanes of this invention can be prepared by techniques wellknown in the art. The actual method used to prepare the polysilanes isnot critical. Suitable polysilanes may be prepared by the reaction oforganohalosilanes with alkali metals as described in Noll, Chemistry andTechnology of Silicones, 347-49 (translated 2d Ger. Ed., Academic Press,1968). More specifically, suitable polysilanes may be prepared by thesodium metal reduction of organo-substituted chlorosilanes as describedby West in U.S. Pat. No. 4,260,780 and West et al. in 25 Polym.Preprints 4 (1984), both of which are incorporated by reference. Othersuitable polysilanes can be prepared by the general procedures describedin Baney, et al., U.S. patent application Ser. No. 4,298,559 which isincorporated by reference.

The polysilane may also be substituted with various metal groups (i.e.,containing repeating metal-Si units). Examples of suitable metals to beincluded therein include boron, aluminum, chromium and titanium. Themethod used to prepare said polymetallosilanes is not critical. It maybe, for example, the method of Chandra et al. in U.S. Pat. No. 4,762,895or Burns et al. in U.S. Pat. No. 4,906,710, both of which areincorporated by reference.

If the preceramic organosilicon polymer is a polycarbosilane, it maycontain units of the type [R₂ SiC], [RSiC₁.5 ], and/or [R₃ SiC] whereeach R is independently selected from the group consisting of hydrogen,alkyl radicals containing 1 to 20 carbon atoms such as methyl, ethyl,propyl etc., aryl radicals such as phenyl, and unsaturated hydrocarbonradicals such as vinyl. Suitable polymers are described, for instance,by Yajima et al. in U.S. Pat. Nos. 4,052,430 and 4,100,233, both ofwhich are incorporated herein in their entirety. Polycarbosilanescontaining repeating (--SiHCH₃ --CH₂₋₋) units can be purchasedcommercially from the Nippon Carbon Co.

The polycarbosilane may also be substituted with various metal groupssuch as boron, aluminum, chromium and titanium. The method used toprepare such polymers is not critical. It may be, for example, themethod of Yajima et al. in U.S. Pat. Nos. 4,248,814, 4,283,376 and4,220,600.

The above organosilicon polymers which contain vinyl groups may bepreferred since vinyl groups attached to silicon provide a mechanismwhereby the organosilicon polymer can be cured prior to sintering. Also,mixtures of any of the above organosilicon compounds are alsocontemplated by this invention.

Specific methods for preparation of suitable organosilicon polymers areillustrated in the examples included in the present specification.

The use of organosilicon polymers as binders for titanium carbide powderis particularly advantageous over binders of the prior art since apolymer can be chosen which will provide a suitable char yield and, ifdesired, additional free carbon. In this manner, the polymer can betailored to obtain a polymer/titanium carbide ratio in the preceramicmixture which is suitable for the molding application utilized

The preceramic organosilicon polymer is generally present in thecompositions of the present invention in the range of about 1 wt % up toabout 50 wt %. Preferably, the polymer is present in the range of about5 wt % up to about 30 wt % and most preferably in the range of about 5to 25 wt. %. The exact amount of polymer, however, is dependent on themethod of molding used. For instance, for standard cold isostaticpressing the preferred amount of polymer is in the range of about 5-20wt. %. On the other hand, for extrusion the preferred amount of polymeris in the range of about 15-25 wt. %.

The compositions of the invention also include titanium carbide powders.These powders are commercially available and well known in the art from,for instance, Starck. Generally, titanium carbide powders with anaverage particle size of less than 10 microns are preferred; powderswith a number average particle size of less than 5 micron are morepreferred; and those with a number average particle size less than 1micron are most preferred.

The compositions of this invention may also contain curing agents whichare used to cause the organosilicon polymer to crosslink prior tosintering. The green bodies produced thereby generally have higherstrengths than the uncured articles and, thus, can better withstand anyhandling or machining processes prior to sintering. These curing agentsare generally activated by heating the green body containing the curingagent to temperatures in the range of 50°-500° C.

Conventional curing agents which are useful in the present invention arewell known in the art. Examples include organic peroxides such asdibenzoyl peroxide, bis-p-chlorobenzol peroxide, bis-2,4-dichlorobenzolperoxide, di-t-butyl peroxide, dicumyl peroxide, t-butyl perbenzoate,2,5-bis(t-butylperoxy)-2,3-dimethyl-hexane and t-butyl peracetate; andplatinum-containing curing agents such as platinum metal, H₂ PtCl₆, and((C₄ H₉)₃ P)₂ PtCl₂. Other conventional curing agents known in the artmay also be used. The curing agent is present in an effective amount,i.e. an amount sufficient to induce crosslinking in the polymer.Therefore, the actual amount of the curing agent will depend on theactivity of the actual agent used and the amount of polymer present.Normally, however, the peroxide curing agent will be present at about0.1 to 5.0 weight percent based on the weight of the compound to becured with the preferred amount being about 2.0 weight percent. Whenplatinum-containing curing agents are used, the amount will normally besuch that platinum is present at about 1 to 1000 ppm based on the weightof the compound to be cured with the preferred amount being about 50 to150 ppm platinum.

In addition to the above curing agent, a crosslinking agent may also beincluded in the mixture to crosslink the polymer and, thereby, modifythe cure characteristics. These agents can include, for example,polyfunctional silanes or siloxanes. The preferred crosslinking agentsare siloxanes with Si-H functional bonds such as Ph₂ Si(OSiMe₂ H)₂ orPhSi(OSiMe₂ H)₃.

The addition of other processing aids such as lubricants, deflocculantsand dispersants is also within the scope of this invention. Examples ofsuch compounds include stearic acid, mineral oil, paraffin, calciumstearate, aluminum stearate, succinic acid, succinimide, succinicanhydride or various commercial products such as Oloa 1200™.

Once the amounts of the various components have been determined, theyare combined in a manner which assures a uniform and intimate mixture sothat areas of varying density throughout the sintered product areavoided. Uniform and intimate mixtures can be prepared by usingconventional blending techniques such as grinding the various powders ineither the dry or wet state or ultrasonic dispersion. Other mixing andgrinding methods will be apparent to those skilled in the art.

The above mixture is then formed into a handleable green body."Handleable green body" as used herein means green bodies which havesufficient green strength to be handled or machined to a desired shapeprior to sintering. Generally, green strengths of 20 is kg/cm² or moremay be obtained in the practice of this invention. This green strengthis achieved primarily because the preceramic mixture includes anorganosilicon polymer which acts as a matrix for the titanium carbidepowder. The increased green strength obtained by the practice of thisinvention alleviates the problems associated with handling fragileobjects and allows for the production of more complex shapes throughmachining, milling etc.

The handleable green bodies may be formed by conventional techniquesknown in the art. Such methods include hot pressing, dry pressing, slipcasting, pressure molding, uniaxial pressing, iso-pressing, extrusion,transfer molding, injection molding, and the like. The present inventionis particularly advantageous in this respect since the amount of polymerin the preceramic mixture can easily be changed to accommodate the useof multiple molding techniques without affecting the quality of thesintered product.

The composition is preferably cured prior to its final shaping. Curingprocedures are well known in the art. Generally, such curing can becarried out by heating the article to a temperature in the range ofabout 50° to 500° C., preferably in an inert atmosphere such as argon ornitrogen.

The shaped green bodies are then fired to an elevated temperature underan inert atmosphere to convert them into ceramic articles havingdensities greater than about 4.2 g/cm³. Upon pyrolysis, theorganosilicon polymers of this invention yield SiC and, optionally, freecarbon. This factor tends to decrease the amount of shrinkage thatoccurs when the mixture is sintered since the SiC forms in theintergranular pores of the titanium carbide powder, thus limiting theshrinkage due to densification. Because less shrinkage occurs, sinteredobjects with increased tolerance control can be formed.

The compositions of this invention may be sintered either under pressureor by using a pressureless process to produce a highly densified ceramicarticle. Since the sintering process employing pressure will generallyproduce ceramic articles with higher density, such a method would bepreferred if maximum density were desired. Generally, however, thepressureless sintering process is preferred because of the simplifiedoperations involved.

Inert atmospheres are used for sintering to prevent oxygen incorporationand silica formation. The sintering process as well as the density ofthe sintered product are thereby enhanced. For purposes of thisinvention, an inert atmosphere is meant to include an inert gas, vacuumor both. If an inert gas is used it may be, for example, argon, heliumor nitrogen. If a vacuum is used it may be, for example, in the range of0.1-200 torr, preferably 0.1-0.3 torr. Exemplary of a combined processmight be firing the composition in argon up to 1200° C., firing from1200° to 1500° C. in a vacuum and firing from 1500° to 2150° C. underargon.

Sintering may be performed in any conventional high temperature furnaceequipped with a means to control the furnace atmosphere. Temperatures ofgreater than 2000° C. are generally used with the preferred range beingabout 2100°-2250° C. The most preferred sintering temperature is about2150° C. Though lower temperatures can be used, the ceramic product maynot possess the desired density.

The temperature schedule for sintering depends on both the volume ofparts to be fired and the composition of the mixture. For smallerobjects the temperature may be elevated relatively rapidly. For largerobjects or those with large concentrations of the organosilicon polymer,however, more extended programs are needed to create uniform ceramicbodies.

The resultant ceramic articles have densities greater than about 4.2g/cm³. It is preferred that the density of the ceramic article begreater than 4.4 g/cm³. The bodies generally have strengths greater than10 kg/m². Such bodies comprise a mixture of mainly titanium carbide withsmall amounts of silicon carbide and carbon being present (eg., lessthan 10% of the total ceramic weight). Generally, the bodies containabout 2-10 wt % (eg., 2-8 wt. %) silicon carbide up to about 2 wt %(eg., 0.1-2 wt %) free carbon and 88-98 wt % titanium carbide. Theexpression "titanium carbide body" is used herein to describe theseceramic bodies.

So that those skilled in the art can better appreciate and understandthe invention, the following examples are given. Unless otherwiseindicated, all percentages are by weight. Throughout this specification"Me" represents a methyl group, "Ph" represents phenyl group, and "Vi"represents a vinyl group.

In the following examples, the analytical methods used were as follows:

Proton NMR spectra were recorded on either a Varian EM360 or FT 200spectrometer and the results presented herein in ppm; fournier transformIR spectra were recorded on a Perkin Elmer 7700 FT spectrometer. Gelpermeation chromatography (GPC) data were obtained on a Waters GPCequipped with a model 600E systems controller, a model 490 UV and model410 Differential Defractometer detectors; all values are relative topolystyrene. TGA and TMA data were recorded on a Du Pont 940thermomechanical analyzer (TMA) and an Omnitherm thermal gravimetricanalyzer (TGA) interfaced to an IBM 386 Computer.

Carbon, hydrogen and nitrogen analysis were done on a Control EquipmentCorporation 240-XA Elemental Analyzer. Oxygen analysis was done on aLeco Oxygen Analyzer equipped with an Oxygen Determinator 316 (Model783700) and an Electrode Furnace EF100. Silicon was determined by afusion technique which consisted of converting the material to solubleforms of silicon and analyzing the solute for total silicon by atomicabsorption spectrometry.

Fired densities were measured by water immersion techniques according toASTM C373-72.

EXAMPLE 1 Pressureless Sintering of Titanium Carbide Powder UsingSiloxane Binder A. Polymer Synthesis

A mixture of 3960 g of PhSi(OMe)₃ and 620 g (ViMe₂ Si)₂ O was added to asolution of 3 g of trifluoromethane sulfonic acid in 800 g of water.After approximately 20 minutes, the solution was refluxed for 5 hours.The solution was cooled and then neutralized with 2.73 g of potassiumcarbonate. The volatiles were removed by distillation until an internaltemperature of 120° C. was reached. The reaction mixture was cooled and1500 g of toluene and 125.7 g of a 3 wt % solution of KOH in water wereadded. The solution was refluxed and the water removed in a Dean-Starktrap. After all of the water was removed, the mixture was cooled and 20mL of Me₂ ViSiCl added. After stirring at room temperature for 2 hours,the mixture was filtered through a 0.2 micron membrane filter and thefiltrate concentrated by rotary evaporation. The residue was dried forabout 1-2 hours at 100° C. and less than 1 torr. The yield was 3053.3 g.

B. Polymer pyrolysis and Char Composition Calculations

A blend of 14.85 g of the resin formed in part A, 5.15 g of Ph₂Si(OSiMe₂ H)₂ and 0.01 g Lupersol™ (bis (t-butylperoxy-2,5-dimethylhexane) was prepared. An aliquot of the blend wascrosslinked at 120° C. for one hour. An aliquot of the crosslinkedpolymer was weighed into a graphite crucible. The crucible wastransferred into an Astro tube furnace. The furnace was evacuated toless than 20 torr and then backfilled with argon. This procedure wasrepeated twice. Under a purge of argon, the sample was heated to 1800°C. at 10° C./minute and held at temperature for 1 hour before cooling toroom temperature. The sample had a mass retention of 44.9%. Theelemental composition of the char was 53.4% carbon. The followingcalculation was made: 100 g of cured polymer gives 44.9 g of a ceramicchar consisting of 20.9 g silicon (46.6 wt. % by difference) and 24 gcarbon (53.4 wt. %). The char consists of 29.9 g of SiC (66.6%) and 15 gC (33.4%). Therefore, every g of polymer gives 0.299 g of SiC and 0.15 gof excess C.

C. Test Bar Fabrication and Firing

A mixture was prepared by mixing 10 g of the resin in section Adissolved in 200 mL toluene, 0.2 g Lupersol™, and 90 g of Starcktitanium carbide powder. The mixture was ultrasonicated for 5 minutesand transferred to a round bottom flask. The solvent was removed invacuo and the residue further dried. The dried powder was ground in amortar and pestle and then sieved through a 90 micron mesh sieve. Thepowder was dry pressed into test bars 35×8×2 mm in a WC lined die with aCarver laboratory press at 3220 kg/cm². The test bars were heated to250° C. for 24 hours to crosslink the polymer. The test bars were firedto 1900°, 2100°, 2150°, or 2250° C. in argon using the followingprogram: room temperature to 1200° C. at 5° C./minute, a 30 minute hold,1200°-1400° C. at 5° C./minute under vacuum, and 1400° C. to final tempat 5° C./min with a 60 minute hold at temperature. The test bars arecharacterized in Table 1.

EXAMPLE 2 Pressureless Sintering of Titanium Carbide Powder UsingSiloxane Binder A. Polymer Synthesis

A mixture of 476 g of PhSi(OMe)₃, 286 g of MeSi(OMe)₃ and 137.5 g (ViMe₂Si)₂ O was added to a solution of 4 g of trifluoromethane sulfonic acidin 400 g of water. After approximately 20 minutes, the solution wasrefluxed for 12 hours. The solution was cooled and then neutralized with3.5 g of potassium carbonate. The volatiles were removed by distillationuntil an internal temperature of 110° C. was reached. The reactionmixture was cooled and 700 g of toluene and 70 g of a 3 wt % solution ofKOH in water were added. The solution was refluxed and the water removedin a Dean-Stark trap. After all of the water was removed, the mixturewas cooled and 27 mL of Me₂ ViSiCl added. After stirring at roomtemperature for 2 hours, the mixture was filtered through a 0.2 micronmembrane filter and the filtrate concentrated by rotary evaporation. Theresidue was dried for about 1-2 hours at 100° C. and less than 1 herr.The yield was 553.3 g.

B. Polymer Pyrolysis and Char Composition Calculations

A blend of 6.554 g of the resin formed in part A and 0.06 g Lupersol™was prepared. An aliquot of the blend was crosslinked at 180° C. for onehour. An aliquot of the crosslinked polymer was weighed into a graphitecrucible. The crucible was transferred into an Astro tube furnace. Thefurnace was evacuated to less than 20 torr and then backfilled withargon. This procedure was repeated twice. Under a purge of argon, thesample was heated to 1800° C. at 10° C./minute and held at temperaturefor 1 hour before cooling to room temperature. The sample had a massretention of 41.8%. The elemental composition of the char was 38.1%carbon and 61.9% silicon (by difference). The following calculation wasmade: 100 g of cured polymer gives 41.8 g of a ceramic char consistingof 25.9 g silicon and 15.9 g carbon. The char consists of 36.97 g of SiC(88.43%) and 4.83 g C (11.57 %). Therefore, every g of polymer gives0.369 g of SiC and 0.048 g of excess C.

C. Test Bar Fabrication and Firing

A mix was prepared using the following procedure: 10 g of the resinprepared in part A, 200 mL of toluene, and 0.20 g Lupersol™ was mixedwith 10 g of Starck titanium carbide powder in a beaker. The mixture wasultrasonicated, dried, ground, sieved, pressed, cured and fired as inExample 1 (except for not firing at 1900° C.). The test bars arecharacterized in Table 1.

EXAMPLE 3 Pressureless Sintering of Titanium Carbide Powder UsingPolysilane Binder A. Polymer Pyrolysis and Char Composition Calculations

A aliquot of commercially available PSS-400 obtained from Shinn NissoKaka Co., Ltd. was weighed into a graphite crucible. The crucible wastransferred into an Astro tube furnace. The furnace was evacuated toless than 20 torr and then backfilled with argon. This procedure wasrepeated twice. Under a purge of argon, the sample was heated to 1800°C. at 10° C./minute and held at temperature for 1 hour before cooling toroom temperature. The sample had a mass retention of 44.2%. Theelemental composition of the char was 42.3% carbon and 57.7% silicon.The following calculation was made: 100 g of cured polymer gives 44.2 gof a ceramic char consisting of 25.5 g silicon and 18.7 g carbon. Thechar consists of 34.6 g of SiC (78.3 %) and 9.58 g C (21.7%). Therefore,every g of polymer gives 0.346 g of SiC and 0.095 g of excess C.

B. Test Bar Fabrication and Firing

A mixture was prepared by mixing 10 g of the resin in section A, 200 mLof toluene and 90 g of Starck titanium carbide powder. The mixture wasultrasonicated, dried, ground, sieved, pressed, crosslinked and fired asin Example 1. The test bars are characterized in Table 1.

EXAMPLE 4 Pressureless Sintering of Titanium Carbide Powder UsingPolycarbosilane Binder A. Polymer Pyrolysis and Char CompositionCalculations

A aliquot of commercially available PCS obtained from Nippon Carbon Co.,Ltd. was weighed into a graphite crucible. The crucible was transferredinto an Astro tube furnace. The furnace was evacuated to less than 20torr and then backfilled with argon. This procedure was repeated twice.Under a purge of argon, the sample was heated to 1800° C. at 10°C./minute and held at temperature for 1 hour before cooling to roomtemperature. The sample had a mass retention of 55.8%. The elementalcomposition of the char was 36.7% carbon and 63.3% silicon. Thefollowing calculation was made: 100 g of cured polymer gives 55.8 g of aceramic char consisting of 63.3 wt % silicon and 37.2 wt % carbon. TheChar consists of 49.9 g of SiC (84%) and 9.5 g C (16%). Therefore, everyg of polymer gives 0.499 g of SiC and 0.090 g of excess C.

B. Test Bar Fabrication and Firing

A mixture was prepared by mixing 10 g of the resin in section A, 200 mLof toluene and 90 g of Starck titanium carbide powder. The mixture wasultrasonicated, dried, ground, sieved, pressed, crosslinked and fired asin Example 1. The test bars are characterized in Table 1.

                  TABLE 1                                                         ______________________________________                                                              Cured  Firing                                                                              Ceramic                                                                              4 pt                                Ex  Binder  %SiC/%C   Density                                                                              Cond. Density                                                                              MOR                                 No  (wt %)  in Body   (g/cm.sup.3)                                                                         (°C.)                                                                        (g/cm.sub.3)                                                                         (kg/m.sup.2)                        ______________________________________                                        1   10      3.62/1.06 3.25   1900  3.99                                                                    2100  4.42    9.9 ±                                                                     0.2                                                              2150  4.43   10.3 ±                                                                     3.4                                                              2250  4.47   11.5 ±                                                                     2.9                                 2   10      4.28/0.22 3.36   2100  4.23    9.9 ±                                                                     0.7                                                              2150  4.33   15.6                                                             2250  4.37   15.7 ±                                                                     5.5                                 3   10      3.86/0.82 3.08   2100  4.31   11.3 ±                                                                     1.1                                                              2150  4.36   16.2 ±                                                                     6.5                                                              2250  4.45   19.4 ±                                                                     3.6                                 4   10      5.23/0.61 3.04   2100  4.21   14.1 ±                                                                     5.3                                                              2150  4.35   14.4 ±                                                                     5.7                                                              2250  4.41   12.8 ±                                                                     5.4                                 ______________________________________                                    

That which is claimed is:
 1. A sintered titanium carbide body consistingessentially of 2-10 wt % silicon carbide, up to 2 wt % free carbon and88 to 98 wt % titanium carbide.
 2. The sintered body of claim 1consisting essentially of 2-8 wt % silicon carbide, 0.1 to 2 wt % freecarbon and 90 to 97.9 wt % titanium carbide.